Process and apparatus for treating heavy oil with supercritical water and power generation system equipped with heavy oil treating apparatus

ABSTRACT

The reforming of heavy oil with supercritical water or subcritical water is accomplished by mixing together supercritical water, heavy oil, and oxidizing agent, thereby oxidizing vanadium in heavy oil with the oxidizing agent at the time of treatment with supercritical water and separate vanadium oxide. The separated vanadium oxide is removed by the scavenger after treatment with supercritical water. In this way it is possible to solve the long-standing problem with corrosion of turbine blades by vanadium which arises when heavy oil is used as gas turbine fuel.

BACKGROUND OF THE INVENTION

The present invention relates to a process and apparatus for treatingheavy oil with supercritical water or subcritical water, therebyreforming heavy oil into light oil. More particularly, the presentinvention relates to a process and apparatus for removing vanadiumcontained in heavy oil at the time of heavy oil reformation. The presentinvention relates also to a power generation system which uses heavy oilas fuel for gas turbines.

It has been common practice to drive gas turbines in thermal electricpower plants by burning gaseous fuel (such as LNG) or light oil (such asgas oil and kerosene). Gas turbines that run on heavy oil are shunnedbecause they are subject to high temperature corrosion by vanadiumcontained in heavy oil; therefore, most gas turbines in practical userun on light oil. One way to cope with this situation is to incorporateheavy oil with magnesium as an additive which forms a high-meltingcomposite oxide of magnesium and vanadium, thereby solidifying vanadiumin the turbine. (See, for example, “Heavy oil combustion gas turbine”,by Nishijima, Journal of Gas Turbine Society of Japan, 11-43, 1983.) Theproblem involved with this method is that the high-melting compositeoxide of magnesium and vanadium (which is called “ash”) sticks toturbine blades, making it necessary to suspend operation for bladecleaning. If vanadium is removed while heavy oil is being reformed intogas turbine fuel, then it would be possible to drive gas turbineseconomically at a low fuel cost.

Reformation of heavy oil into gas turbine fuel is accomplished by use ofsupercritical water which decomposes and cracks hydrocarbons in heavyoil, thereby yielding combustible gas. Reaction of heavy oil withsupercritical water and alkali is also known as a means to remove sulfurcomponents from heavy oil. Processes for reforming heavy oil withsupercritical water or subcritical water are disclosed in JapanesePatent Laid-open Nos. 6-279763, 10-310780, 11-80750, 11-166183,11-246876, 2000-109850, 2000-109851, and 2001-50010.

The prior art techniques mentioned above disclose nothing about thetreatment of vanadium contained in heavy oil. If vanadium is removedfrom heavy oil before heavy oil is introduced into the gas turbinecombustor, then it would be unnecessary to solidify vanadium aftercombustion and hence it would be unnecessary to suspend operation forblade cleaning.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process andapparatus for treating heavy oil in such a way that vanadium containedin heavy oil is isolated from heavy oil while heavy oil is beingreformed by treatment with supercritical water or subcritical water.

It is another object of the present invention to provide a powergeneration system which is equipped with said heavy oil treatingapparatus so as to obviate the necessity of adding magnesium to gasturbine fuel and the necessity of cleaning turbine blades of ashsticking thereto.

The process according to the present invention consists of mixingtogether vanadium-containing heavy oil, water, and oxidizing agent, andreacting them under the condition that said water attains thesupercritical state or subcritical state, thereby reforming heavy oiland oxidizing vanadium. Vanadium oxide resulting from reaction betweenvanadium and oxidizing agent is subsequently removed by a vanadium oxidescavenger.

The reaction of heavy oil, water, and oxygen should preferably becarried out at a temperature of 350-600° C. under a pressure of 20-50MPa. The reaction time should be 10 seconds to 1 hour. The mixing ratio(by volume) of water to heavy oil should be from 0.1:1 to 4:1. Theamount of the oxidizing agent should be enough to oxidize vanadium intoV205. The molar ratio of oxidizing agent to vanadium should be higherthan 1.0, and the weight ratio of oxidizing agent to heavy oil should besmaller than 10%.

The oxidizing agent should preferably be at least one species selectedfrom the group consisting of oxygen, air, hydrogen peroxide aqueoussolution, nitric acid, and nitrates. The vanadium oxide scavenger shouldbe at least one species selected from the group consisting of iron oriron compounds, calcium or calcium compounds, activated carbon, solidcarbon compounds, aluminum oxide, and silicon oxide.

The oxidizing agent may be added to high-temperature high-pressure waterin the supercritical state or subcritical state. Alternatively, theoxidizing agent may be added to water which is not in the supercriticalstate or subcritical state and then water is heated under pressure sothat it attains the supercritical state or subcritical state.

According to the present invention, the heavy oil treating processconsists of a step of adding an oxidizing agent to high-temperaturehigh-pressure water in the supercritical state or subcritical state, astep of mixing said high-temperature high-pressure water containing saidoxidizing agent with vanadium-containing heavy oil, a step of reformingsaid heavy oil and oxidizing vanadium with said oxidizing agent, and astep of bringing a vanadium oxide scavenger into contact with thereformed oil which contains vanadium oxide resulting from oxidation ofvanadium by said oxidizing agent, thereby removing vanadium oxide fromsaid reformed oil.

Alternatively, the heavy oil treating process consists of a step ofadding an oxidizing agent to water, a step of mixing said watercontaining said oxidizing agent with vanadium-containing heavy oil, astep of heating under pressure the mixture of said oxidizing agent, saidwater, and said heavy oil so that said water attains the supercriticalstate or subcritical state, thereby reforming said heavy oil andoxidizing vanadium, and a step of bringing a vanadium oxide scavengerinto contact with the reformed oil which contains vanadium oxideresulting from oxidation of vanadium by said oxidizing agent, therebyremoving vanadium oxide from said reformed oil.

According to the present invention, the heavy oil treating apparatus hasa reactor for reacting heavy oil with high-temperature high-pressurewater in the supercritical state or subcritical state, thereby reformingsaid heavy oil and yielding reformed oil, wherein the reactor isprovided with an oxidizing agent supplying unit to supply an oxidizingagent thereto and is also provided with a vanadium oxide capturing unitto bring a vanadium oxide scavenger into contact with said reformed oildischarged from said reactor, thereby removing vanadium oxide containedin said reformed oil.

Alternatively, the heavy oil treating apparatus has a reactor forreacting heavy oil with water in the supercritical state or subcriticalstate, thereby reforming said heavy oil, a water supplying pipe tosupply water in the supercritical state or subcritical state to saidreactor, a heavy oil supplying pipe to supply heavy oil to said reactor,an oxidizing agent adding apparatus to add an oxidizing agent to waterin the supercritical state or subcritical state flowing in said watersupplying pipe, and a vanadium oxide capturing unit to bring a vanadiumoxide scavenger into contact with the treated product discharged fromsaid reactor, thereby removing vanadium oxide contained in said treatedproduct.

The heavy oil treating apparatus of the present invention may be ofmulti-tubular type consisting of a plurality of reactors and have avanadium oxide capturing apparatus into which the treated productdischarged from said reactors is introduced to remove vanadium oxide.This construction is desirable for efficient treatment. More than oneset of such apparatus may be installed.

The present invention is directed also to a power generation systemwhich comprises having the heavy oil treating apparatus constructed asmentioned above in part of the fuel supply system and producing electricpower in such a way that said heavy oil treating apparatus suppliesreformed fuel to a combustor, which evolves combustion gas, which issupplied to a gas turbine, which drives a generator connected thereto.

The power generation system also comprises a waste heat recoveringboiler to recover waste heat from exhaust gas discharged from said gasturbine, thereby raising the water temperature, and piping to supplypart of high-temperature high-pressure water or steam evolved by saidwaste heat recovering boiler to said reactor of said heavy oil treatingapparatus.

The feature of the present invention is that vanadium is released fromcyclic hydrocarbon compounds or porphyrin structure in heavy oil bymeans of supercritical water or subcritical water which functions as anorganic solvent. The reaction to remove vanadium is promoted by anoxidizing agent added to the reaction system.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent fromthe following description of embodiments with reference to theaccompanying drawings in which:

FIG. 1 is a schematic diagram showing one embodiment of the heavy oilreforming apparatus used in the present invention;

FIG. 2 is a schematic diagram showing one embodiment of the heavy oiltreating apparatus according to the present invention;

FIG. 3 is a schematic diagram showing another embodiment of the heavyoil treating apparatus according to the present invention;

FIG. 4 is a schematic diagram showing one embodiment of the gas turbinepower generation system to which is connected the heavy oil treatingapparatus of the present invention;

FIG. 5 is a diagram showing one example of vanadium compound in heavyoil;

FIG. 6 is a diagram showing a result of the experiment on removal ofvanadium from heavy oil;

FIG. 7 is a diagram showing the possible mechanism of reaction to removevanadium from heavy oil;

FIG. 8 is a diagram showing the effect of additives on the ratio ofremoval of vanadium from heavy oil;

FIG. 9 is a plan view of the heavy oil treating apparatus in anotherexample of the present invention; and

FIG. 10 is a side elevation of the heavy oil treating apparatus inanother example of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Vanadium in heavy oil exists in the form of porphyrin complex or cyclicorganic compound as shown in FIG. 5. (Fish, R. H., Komlenic, J. J.,Anal. Chem. 1984, 56(3), p. 510-517). High-temperature high-pressurewater in the supercritical state or subcritical state disperses organicmolecules into supercritical water or subcritical water which has asolvent action, and also decomposes organic molecular chains throughhydrolysis. However, supercritical water or subcritical water alone doesnot decompose vanadium compounds in organic molecules. Vanadium is notdecomposed by alkali. This is different from the desulfurizing reactionaccording to the conventional technique.

According to the present invention, heavy oil is mixed withhigh-temperature high-pressure water in the supercritical state orsubcritical state and then the resulting mixture is incorporated with anoxidizing agent. This procedure releases vanadium from organic moleculesby decomposition. FIG. 6 shows the ratio of vanadium removed which isachieved when heavy oil, water, and hydrogen peroxide aqueous solutionare reacted together at a high temperature under a high pressure. It isnoted that the ratio of vanadium removed increases as the temperatureincreases. Presumably, the removal of vanadium involves the followingreactions that take place simultaneously. (1) Partial oxidation oforganic hydrocarbons. (2) Generation of hydrogen by shift reactionbetween CO and water. (3) Attack of CO to oxygen in organic molecules.(4) Cleavage of organic molecule chains by hydrogen and water. (5)Oxidation of vanadium by the oxidizing agent. These reactions decomposevanadium in organic molecules and releases vanadium in the form ofvanadium oxide.

The vanadium oxide (V205) resulting from the above-mentioned reactionsis removed from the reformed oil by adsorption or reaction with ascavenger. Adsorption of vanadium oxide may be accomplished by physicaladsorption with activated carbon or by chemical adsorption with aninorganic compound used for catalyst production. Since vanadium oxidereacts with a metal such as calcium and iron to give a composite oxide,these metals can be used as a scavenger to remove vanadium from heavyoil. Once caught by the scavenger, the resulting solid is dischargedfrom the system and then separated into vanadium and scavenger to berecycled.

FIG. 8 shows the effect of supercritical water on the ratio of vanadiumremoved from heavy oil.

The results were obtained by experiments under the following conditions.Temperature: 420° C., pressure: 25 MPa, water/oil ratio: 1.0, amount ofvanadium in heavy oil: 20 ppm, and concentration of additive: 1%. It isnoted that hydrogen peroxide produces a remarkable effect of removingvanadium.

First Embodiment

FIG. 1 shows a part of the heavy oil treating apparatus according to thepresent invention. This part is designed for heavy oil reformation. Themixer 1 (for water, heavy oil, and oxidizing agent) functions as theinlet of the treating apparatus. To the mixer 1 are connected a watersupply pipe 2 to supply high-temperature high-pressure water, a heavyoil supply pipe 3 to supply heavy oil, and an oxidizing agent supplypipe 4 to supply an oxidizing agent to high-temperature high-pressurewater flowing in the water supply pipe 2. The mixer 1 mixes togetherwater and heavy oil by the solvent action of supercritical water orsubcritical water. The resulting mixed fluid is sent to the reactor 5.The mixing of high-temperature high-pressure water, heavy oil, andoxidizing agent may be accomplished by any of simple confluence method,circular flow method, and countercurrent method. An alternativeconstruction is permissible in which the mixer 1 is omitted and thereactor 5 is supplied directly with high-temperature high-pressurewater, heavy oil, and oxidizing agent.

The reactor 5 permits reactions (shown in FIG. 7) to proceed so thatvanadium in heavy oil is released from organic molecule. For thesereactions to proceed, it is necessary to keep the entire system at aprescribed temperature and pressure. One way to achieve this object isto supply previously heated and pressurized water as in this embodiment.The other way is to supply the mixer 1 or the reactor 5 with water andheavy oil and heat and pressurize them later. Reactions in the reactor 5give rise to reformed fuel containing released vanadium oxide (fluid 7),which is discharged from the outlet 6 (for reformed fuel oil).

FIG. 2 shows another embodiment of the heavy oil treating apparatusaccording to the present invention in which the apparatus shown in FIG.1 is supplemented with a system to remove vanadium oxide from reformedfuel.

The fluid containing reformed fuel and released vanadium oxide (fluid 7)leaves from the outlet 6, passes through the connecting pipe 8, andenters the vanadium oxide catcher 9 in which vanadium oxide isseparated. An alternative construction is permissible in which theconnecting pipe 8 is omitted and the reactor 5 is connected directly tothe vanadium oxide catcher 9. The vanadium oxide catcher 9 is filledwith the vanadium oxide scavenger 10 to catch vanadium oxide. Thevanadium oxide scavenger 10 collects vanadium oxide from the fluid 7 byadsorption or reaction. The vanadium oxide catcher 9 collects onlyvanadium oxide and discharges almost all hydrocarbons as reformed fuel11.

The vanadium oxide scavenger 10 is held as a fixed bed or fluidized bedin the vanadium oxide catcher 9. In the former case, the vanadium oxidescavenger may be fixed to the grating; in the latter case, the vanadiumoxide scavenger may be formed into pellets with an adequate diametermatching the terminal velocity (which is larger than the linear velocityof the fluid 7). Alternatively, the vanadium oxide scavenger may take ona platy or honeycomb form through which the fluid 7 passes. The vanadiumoxide catcher 9 may be provided with a system to discharge used vanadiumoxide scavenger or to replenish fresh vanadium oxide scavenger becausethe vanadium oxide scavenger 10 becomes gradually less effective withtime. Alternatively, the reactor 5 may be equipped with more than onevanadium oxide catcher 9 so that the catchers are switched sequentiallyor the catchers are partly suspended at a certain interval.

Second Embodiment

FIG. 3 shows another heavy oil treating apparatus according to thepresent invention. This apparatus is identical to that shown in FIG. 2in the structure covering the reactor 5 to the vanadium oxide catcher 9.With vanadium oxide removed by the vanadium oxide catcher 9, thereformed fuel 11 is discharged as shown in FIG. 3. The outlet of thevanadium oxide catcher 9 is provided with a particle collector 28 ofcyclone type to collect the vanadium oxide scavenger in particulate formwhich might be present in the reformed fuel 11. The particle collector28 may be replaced by a filter. Alternatively, the particle collector 28may be provided with a means to return the collected vanadium oxidescavenger 10 to the vanadium oxide catcher 9.

Third Embodiment

FIGS. 9 and 10 show further another heavy oil treating apparatusaccording to the present invention. FIG. 9 is a plan view and FIG. 10 isa side elevation.

The apparatus in this embodiment is characterized in having a pluralityof tubular reactors 5. The reactors 5 are supplied with a mixture ofoxidizing agent and high-temperature high-pressure water through themanifold 30. The manifold 30 branches into a plurality of branch pipes32 to which the reactors 5 are connected. In the case shown in FIGS. 9and 10, six reactors are connected to each branch pipe. As shown in FIG.10, the mixture of oxidizing agent and high-temperature high-pressurewater which has been introduced into the branch pipe 32 enters the topof each of the six reactors.

On the other hand, heavy oil is introduced into the manifold 31. Themanifold 31 branches into a plurality of branch pipes 33 to which thereactors 5 are connected. Thus, heavy oil introduced into one branchpipe 33 is distributed into a plurality of rectors. As shown in FIG. 10,the heavy oil enters the top of the reactor 5.

Each branch pipe 32 supplies high-temperature high-pressure water andoxidizing agent to the six reactors, and each branch pipe 33 suppliesheavy oil to the six reactors. The heavy oil is reformed in thereactors, and the treated product is discharged from the bottom of thereactor and introduced into the manifold 34. The treated product issubsequently introduced into the vanadium oxide catcher 9 for removal ofvanadium oxide.

According to this embodiment, it is possible to treat a large amount ofheavy oil efficiently at one time. Thus the system of this embodiment isof great practical use.

Fourth Embodiment

FIG. 4 shows a gas turbine power generation system which is equippedwith the heavy oil treating apparatus of the present invention. In thefirst and second embodiments, it is assumed that the reformed fuel 11 isstored or transported for use at power generation plants. Thisembodiment is designed such that the reformed fuel is immediately burnedin the combustor 20 of the power generation system.

As in the first and second embodiments, the mixer 1 mixes togetherhigh-temperature high-pressure water, heavy oil, and oxidizing agent,the reactor 5 oxidizes vanadium into vanadium oxide for separation fromheavy oil, and the vanadium oxide catcher 9 captures vanadium oxide fromreformed fuel 11 with the aid of vanadium oxide scavenger 10. The usedscavenger 12 is partly removed before the action of the vanadium oxidescavenger 10 becomes saturated. The used scavenger 12 which has beenremoved is sent to the scavenger cleaner 13 in which the scavenger isrefreshed by cleaning and reaction to remove vanadium oxide. Therefreshed scavenger 15 is recycled to the scavenger supply system. Atthis time, new scavenger 16 is added to replenish the loss by reactionand returned to the vanadium oxide catcher 9. In this embodiment, oneeach of the reactor 5 and the vanadium oxide catcher 9 are installed;however, more than one each of the reactor 5 and the vanadium oxidecatcher 9 may be installed so as to ensure an adequate residence timefor the reaction of the fuel to be supplied to the gas turbine combustor20 and the capture of vanadium oxide. The reformed fuel is burned in thecombustor 20 with the aid of air 19 compressed by the compressor 18. Thecombustion gas 21 drives the turbine 22 connected to the dynamo 23 forpower generation.

The gas turbine exhaust gas 24 discharged from the gas turbine transfersheat to water 26 in the exhaust gas heat exchanger 25 and generateshigh-temperature high-pressure water which is returned to the reactor 5through the water supply pipe 2. Finally, the gas turbine exhaust gas isdischarged from the chimney stack 27. Utilization of heat of exhaust gasfrom the gas turbine improves the efficiency of the system.

This embodiment may be modified such that exhaust gas recovery boilerare installed before and after the exhaust gas heat exchanger 25, as inthe conventional gas turbine compound power generation system, so thatsteam thus generated drives a steam turbine to generate electric power.In addition, the system in this embodiment may be supplemented with adenitrating unit to remove nitrogen oxide evolved at the time ofcombustion in the gas turbine combustor or with a desulfurizing unit toremove sulfur oxide evolved at the time of combustion. In thisembodiment, vanadium in heavy oil is removed by the vanadium oxidecatcher 9, so that there is no possibility of the gas turbine undergoinghigh-temperature corrosion. Therefore, it is not necessary to add anadditive like magnesium to form composite oxides with vanadium. In thisway it is possible to prevent metal oxide ash from sticking to turbineblades, thereby permitting continuous operation as in the case of thegas turbine system which runs on light oil fuel. This leads to a highplant operation rate and efficient power generation.

This embodiment solves the problem with corrosion of the gas turbine byvanadium oxide which was encountered in the conventional heavy oilcombustor.

According to the present invention, it is possible to separate vanadiumfrom heavy oil in the reforming of heavy oil with supercritical water orsubcritical water. Vanadium oxide isolated from reformed oil is capturedby the vanadium oxide scavenger. Thus, according to the presentinvention, it is possible to solve the long-standing problem withcorrosion of turbine blades by vanadium which arises when heavy oil isused as gas turbine fuel.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

1-8. (canceled)
 9. A heavy oil treating apparatus having a reactor forreacting heavy oil with high-temperature high-pressure water in thesupercritical state or subcritical state, thereby reforming said heavyoil and yielding reformed oil, which comprises an oxidizing agentsupplying unit to supply an oxidizing agent to said reactor and avanadium oxide capturing unit to bring a vanadium oxide scavenger intocontact with said reformed oil discharged from said reactor, therebyremoving vanadium oxide contained in said reformed oil.
 10. A heavy oiltreating apparatus having a reactor for reacting heavy oil with water inthe supercritical state or subcritical state, thereby reforming saidheavy oil, a water supplying pipe to supply water in the supercriticalstate or subcritical state to said reactor, and a heavy oil supplyingpipe to supply heavy oil to said reactor, which comprises an oxidizingagent adding apparatus to add an oxidizing agent to water in thesupercritical state or subcritical state flowing in said water supplyingpipe and a vanadium oxide capturing unit to bring a vanadium oxidescavenger into contact with the treated product discharged from saidreactor, thereby removing vanadium oxide contained in said treatedproduct.
 11. A heavy oil treating apparatus as defined in claim 9,wherein said oxidizing agent is at least one species selected from thegroup consisting of oxygen, air, hydrogen peroxide aqueous solution,nitric acid, and nitrates.
 12. A heavy oil treating apparatus as definedin claim 9, wherein said vanadium oxide scavenger is at least onespecies selected from the group consisting of iron or iron compounds,calcium or calcium compounds, activated carbon, solid carbon compounds,aluminum oxide, and silicon oxide.
 13. A power generation system whichcomprises having the heavy oil treating apparatus defined in claim 9 inpart of the fuel supply system and producing electric power in such away that said heavy oil treating apparatus supplies reformed fuel to acombustor, which evolves combustion gas, which is supplied to a gasturbine, which drives a generator connected thereto.
 14. A powergeneration system as defined in claim 13, which comprises a waste heatrecovering boiler to recover waste heat from exhaust gas discharged fromsaid gas turbine, thereby raising the water temperature, and piping tosupply part of high-temperature high-pressure water or steam evolved bysaid waste heat recovering boiler to said reactor of said heavy oiltreating apparatus.
 15. A heavy oil treating apparatus as defined inclaim 9, which is of multi-tubular type consisting of a plurality ofsaid reactors and which has said vanadium oxide capturing apparatus intowhich the treated product discharged from said reactors is introduced toremove vanadium oxide.
 16. A heavy oil treating apparatus as defined inclaim 10, wherein said oxidizing agent is at least one species selectedfrom the group consisting of oxygen, air, hydrogen peroxide aqueoussolution, nitric acid, and nitrates.
 17. A heavy oil treating apparatusas defined in claim 10, wherein said vanadium oxide scavenger is atleast one species selected from the group consisting of iron or ironcompounds, calcium or calcium compounds, activated carbon, solid carboncompounds, aluminum oxide, and silicon oxide.
 18. A power generationsystem which comprises having the heavy oil treating apparatus definedin claim 10 in part of the fuel supply system and producing electricpower in such a way that said heavy oil treating apparatus suppliesreformed fuel to a combustor, which evolves combustion gas, which issupplied to a gas turbine, which drives a generator connected thereto.19. A power generation system as defined in claim 18, which comprises awaste heat recovering boiler to recover waste heat from exhaust gasdischarged from said gas turbine, thereby raising the water temperature,and piping to supply part of high-temperature high-pressure water orsteam evolved by said waste heat recovering boiler to said reactor ofsaid heavy oil treating apparatus.
 20. A heavy oil treating apparatus asdefined in claim 10, which is of multi-tubular type consisting of aplurality of said reactors and which has said vanadium oxide capturingapparatus into which the treated product discharged from said reactorsis introduced to remove vanadium oxide.